Kinetics, compositions and structures of carbon dioxide/hydrogen hydrate formation in the presence of cyclopentane

Abstract

Cyclopentane(CP) as an efficient promoter has not been evaluated for capturing CO2 form fuel gas via forming hydrate. The work systematically studies the kinetics and CO2 recovery of gas (40.0 mol% CO2 + 60.0 mol% H2) hydrate formation in the presence of CP at 276.15 K and 6.0 MPa. Meanwhile, X-ray diffraction and Raman spectrum were adopted to determine the hydrate structure and composition. The results showed that there were two steps for hydrate formation in the system, Step 1: Pure CP hydrates formation. Step 2: Gas molecules trapped in hydrate cages to form CP/gas (CO2, H2) mixed hydrates. Besides, the CO2 recovery of up to 98.8% was obtained at gas-liquid ratio of 5/6 and CP volume concentration of 23.4 vol%, indicating that almost all CO2 could be removed from fuel gas by one-stage of hydrate formation. In addition, not only CP/gas (CO2, H2) mixed hydrates (sII) but also pure CO2 hydrates (sI) are observed in the system. Strikingly, the work confirms that some of H2 molecules are also trapped in the hydrate phase, and its amount increased as the CP volume concentration increase. From the view point of cost-effective and H2-saving, the gas-liquid ratio of 5/6, CP volume concentration of 3.0 vol% and precooling liquid are the optimum conditions for HBGS.